For the discovery of dynamite and other cognate powerful explosives, which have now become inseparable handmaids of the mining and engineering industries, the world owes a debt of gratitude to the late Alfred Nobel, the famous Swedish scientist and chemist, since he was the first to turn to practical purposes at his laboratory at Heleneborg, near Stockholm, the powerful blasting agent nitro-glycerine, discovered by Sobriero, and colloquially known as "blasting oil." This compound, owing to its extremely dangerous nature and the frequency of the accidents attending its use, was prohibited in many of the leading countries; and Nobel realizing these numerous disadvantages, concerted his energies for a considerable time in the quest for an agent with which the nitro-glycerine could be combined, and which while not deteriorating in the slightest its high explosive qualities, would at the same time enable it to be handled with comparative impunity. In this search he was ultimately successful by mixing the nitro-glycerine with an absorbent earth called "kieselguhr," and producing the compound now known as dynamite. The result of this discovery was an immediate expansion in the employment of the explosive for blasting purposes in all parts of the world. After establishing factories in Germany and France in 1871, Nobel went to Great Britain, where he established his future home, and also founded what is now one of the greatest and most flourishing British industries and the largest explosive works in the world. Nobel himself selected the site for his proposed factory, and his ultimate choice fell upon Ardeer on the west coast of Scotland. A more suitable spot for the prosecution of a dangerous trade could scarcely have been found, as the natural configuration of the country is a series of waste sand dunes, which lend themselves admirably to the work in hand by serving as natural barriers between the various sections of the danger zone. The factory covers an area of over 800 acres, occupied by more than 800 different buildings. The works are entirely self-contained, and thus a number of different subsidiary industries are embraced in the isolated colony established at a barren spot on the shores of the Atlantic. Nitro-glycerine, as is well known, is a combination of glycerine and a mixture of sulphuric and nitric acids. The former is brought from all parts of the world, and upon arrival is subjected to a rectifying process, by which the various impurities suspended in the fluid are removed. The nitric acid is prepared in large buildings, in which are ranged long rows of retorts bricked up like ovens. These retorts are charged with sulphuric acid and nitrate of soda, and immediately the two compounds come into contact a chemical action commences, the nitric acid being released as a corrosive gas. The latter is carried through pipes on to a series of earthenware jars and other condensing apparatus, into which the gas is discharged and condensed. The nitric acid thus obtained is further mixed with sulphuric acid, also produced in extensive works on the spot, and conveyed in steel cars hauled by ponies to a station at the foot of one of the nitro-glycerine "hills," as the mounds in which this powerful explosive liquid is prepared are called. There are five of these "hills," comprising lofty earth embankments, within which are located the buildings in which the manufacture is carried out. The provision of the surrounding mounds covered with tall rank grass serves to arrest the flight of fragments of the structure within, and the concussion produced by an explosion should the building within from any cause "blow up." The hills are pierced in all directions with tunnels, by which means communication with the secluded buildings is maintained. When the cars filled with acids reach the foot of one of the hills, they are thence transported to the top by cable haulage. In the "danger area" the severest discipline is maintained. All entrances are carefully guarded by searchers, who rigorously examine every individual that desires to enter, relieving him of any metallic objects that may be cavried upon his person, together with matches and other suspicious objects, which upon coming into contact with the dangerous chemicals used in this zone might provoke serious trouble. No matter how often an employee engaged within the hill may pass in and out, every time he enters he must submit to this preliminary and essential operation. There are also some 500 girls employed, and these are under the charge of matrons. Hair pins, ordinary pins, shoe buttons, metal pegs within the soles of the shoes, knitting and other needles are all religiously barred. Their hair is tied with braid or ribbon, and as with the male employees, every time they enter the danger area they are similarly searched by the matrons. Within the danger area the various employees en gaged in the different departments or phases of worJK are garbed in special non-inflammable working suits, varying in color according to their respective occupations. Each operator is strictly forbidden to venture 476 beyond the confines of his own department except by special order, and any disobedience of this regulation can be immediately descried by the distinctive dress by one of the many superintendents at any distance. The type of dress adopted has mainly the object of preserving the workers from burns by powder taking fire, as wool is not readily ignited, and to prevent the introduction of foreign matters, as they have no pockets. A nitro-glycerine hill is approximately 60 feet in height. It screens in recesses several frail structures built of wood painted white and roofed with flaring red canvas. These are the nitrating and washing houses, and they are so arranged that the nitro-glycerine, after each progressive stage, can run by gravitation to the succeeding operation. The floor is covered with sheet lead, and the feet of all who enter the building are incased in heavy thick overshoes of rubber, since no shoe that has trodden the ground outside is permitted to touch the floor in a danger building, as thereby grit might be introduced, the subsequent friction of which might produce a spark, and fire the explosive contents of the building. In each of the nitrating houses are two huge cylindrical leaden tanks with dome-shaped tops, five feet in diameter by six feet in depth. Beside the vat is seated the operative, with his eye glued to a thermometer extending into the interior of the cylinder. This thermometer is five feet in length, and only the upper part is visible, that containing the mercury bulb extending down into the chemical contents. The vat is charged with sulphuric acid mixed with nitric acid. The glycerine is admitted in the fcrm of a fine spray, the jet being maintained by compressed air. The vat is entirely incased by a jacket, through which currents of ice-cold water are continually rushing, while similarly within the vat are four concentric coils of lead pipes, through which cold water circulates. The full charge within the cylinder of the nitric and sulphuric acids has to be supplied with 900 pounds of glycerine, and this operation is one of the most critical during the whole process of manufacture, being attended by the ever-present danger of spontaneous explosion. The chemical combination of the glycerine with the acids results in the generation of intense heat, the glycerine as rapidly as it enters the chamber seizing the nitric acid, thereby combining to form nitro-glycerine, while, the sulphuric acid instantly absorbs the water which is released. It will thus be seen that it is imperative that the heat generated should be maintained within certain limits. The maximum allowed is 22 deg. C. (72 deg. F.). Should too much glycerine, however, be fed in, the heat is liable to rise above the danger point, which fact is immediately revealed to the operator by the thermometer. The inflow of glycerine is instantly reduced or cut off, and a greater supply of air admitted within the vat. By such means, however, it is not always possible to arrest the action, and therefore, should the thermometer continue to rise slowly, the man gives a warning shout to his comrade below to "stand by." Should the heat still increase, he cries, "Let her go." The man below immediately opens a valve in the base of the cylinder, and the whole charge is swept quickly away, and the coming explosion killed in an excess of water in a special drowning tank. It is, however, not always possible to give warning of the impending danger. The heat may rise very rapidly and resist control, in which event the operator without any preliminary notice to his comrade simply shouts a warning to pull open the valve and runs to a place of safety, while the charge is instantly swept into the drowning tank. The process of combination occupies about one hour, and at the end of this time the 900 pounds of glycerine has been convert- ed to more than double the weight of nitro-glycerine. The compound now flows downward to the next compartment, where it has to be separated from the spent acids. It runs down a leaden gutter into a tank about eight feet in length by two feet in width, and when the tank is fully charged, the contents are allowed to stand for a little while. The nitro-glycerine being lighter than the acid rises to the surface like oil on water, and is then skimmed off by means of a large aluminium ladle and poured into a pocket at one end of the tank, whence it flows away through a pipe to the washing tank. It is first washed with cold and afterward with warm water and carbonate of soda. In a final washing house the nitro-glycerine is freed from every trace of acidan imperative proceeding, since the slightest trace of this agent might at some time or another set up chemical action and heat culminating in an unexpected explosion. A sample f each charge of nitro-glycerine made is taken, in order to detect the presence or otherwise of acid by litmus paper and other tests. If satisfactory the product is ready for further operations, but if still containing traces of acid, further washing is necessary. After leaving the washing departments the nitroglycerine has finally reached the bottom of the hill, where it is made into dynamite. This apartment, like its fellows, is built of thin wood and the floor covered with lead. On either side is a low table, with the mixing box in which the kieselguhr is combined with the liquid nitro-glycerine. This absorbent earth is mainly composed of the skeletons of mosses and microscopic diatoms found in the black slaty peat of Scotland, Germany, Italy, and other countries. Upon its arrival at the factory it is first calcined in a guhr kiln, rolled, and sifted into the consistency of flour and is of a light pink color. The dynamite is composed in the approximate proportions: nitro-glycerine 75 pounds, guhr 25 pounds, and some carbonate of ammonia. The nitro-glycerine is poured into a small square wooden box about 3 feet square by 18 inches deep, containing the other ingredients, given a preliminary mix so that the liquid may be entirely absorbed, and conveyed to the mixing department by a runner. The mixing operation is carried out by women, who knead and mix the ingredients together with their hands as if it were dough, the operation being carried out with complete thoroughness. The mixture is then picked up by a big wooden scoop and dumped into a sieve with brass meshes. The dynamite is rubbed through the orifices in small particles. As it passes through the sieve it resembles a greasy coffee-colored earth, finely divided, and the combination of the constituent parts being completely accomplished, the product is ready for the manufacture of cartridges. This work is also carried out by female labor. The cartridge houses are long rows of single cabins about 10 feet in length, and the same in width. All the buildings for the various phases of the work are divided into small units accommodating from four to six persons. In the cartridge house the machines are attached to the two side walls. They comprise a conical hopper into which the dynamite is placed, and a small vertical brass rod or piston actuated by a lever resembling a pump handle. At the base of the hopper is a small brass tube in which the plunger slides. As the piston descends into the mass of dynamite contained in the hopper, it forces the requisite quantity through the brass tube at the bottom into the cartridge wrapper, which the girl has twisted round the tube and holds in one hand. When the charge, about three inches in length, has been inserted in the wrapper, the latter is removed, the top folded down, and the finished cartridge dropped tnrough a slot in the wall, whence it falls into a special receiver placed outside. The operator replenishes the supply of dynamite within the hopper from a box of loose dynamite placed outside the hut through a similar slot by means of a wooden spoon. The process of filling the cartridges is carried out with great rapidity, the result of continued practice, while the plunger of the filler is lubricated by the nitro-glycerine itself. In another hut blasting gelatine cartridges are made, the process being somewhat different. This explosive is 50 per cent more powerful than ordinary dynamite. It is of the consistency of tough elastic paste, and comprises about 7 per cent of nitro-cotton to 93 per cent of nitro-glycerine. The material is forced through a sausage machine, and as it issues therefrom it is chopped into three-inch lengths by a wooden wedge upon an India-rubber covered table, and wrapped into cartridges with almost lightning speed. There are in all seventy of these cartridge huts. Owing to the fact that nitro-glycerine congeals at 43 deg. F. and freezes at 40 deg. F., it is necessary to maintain the atmosphere within the buildings at an even warm tern- 477 perature. Steam heating is employed, the minimum temperature being 50 deg. F., the radiating pipes being completely and carefully inclosed, so that no loose explosive may come into contact with the hot steam pipes, and possibly promote decomposition. An extensive variety of explosives is prepared at these works, suitable for the various exigencies of commerce and war. The principal comprise various forms of gelatines and dynamite, such as guhr dynamite, blasting gelatine, gelatine dynamite, and gelignite, the latter two combinations of nitro-glycerine, nitro-cotton, nitrate of potash, and wood meal. The gelatine explosives are peculiarly adapted for submarine work, as they are entirely unaffected by wet or moisture of any kind. There are also produced the "Monobel powder" and "carbonite," which are specially designed for use in fiery coal mines, as they contain a lower proportion of nitro-glycerine than dynamite, and, in addition, cooling mixtures. One of the greatest outputs of these works is gun-cotton in several varieties, either in its pure state or combined with nitro-glycerine, as "cordite" and "bal-lastite," or with blasting gelatine. The fundamental constituent is made from cotton waste, the material being the residue left on the spindles. The waste before use is shredded, cleaned to remove all dirt, grease, and other foreign substances, then carded and pulped, so that at last it is rendered a perfectly homogeneous substance. It is then ready for conversion into either insoluble guncotton or soluble nitro-cotton. The process of nitration is carried out in small iron pans in large, lofty, single-floored buildings. The pans are jacketed during the nitration by standing them in long iron coolers. Running along the coolers are the acid taps, whence the requisite supplies are obtained. Four pounds of cotton are placed in a pan with 115 pounds of mixed sulphuric and nitric acids. The chemical combination is completed in a few minutes, or may take several hours, depending upon the quality desired, and the acids are then poured off while the desired quality of nitro-cotton is ready for its first washing. Until the nitro-cotton has had every trace of the acid removed, the danger of spontaneous combustion is ever-present. It is no uncommon circumstance for the substance to flare up as the operator empties the contents of the centrifugal acid separator. No harm, however, results beyond the possible singeing of the eyebrows and the emission of a column of noxious smoke. The washing process is therefore most thorough in character. Not only are the contents whirled and tossed about in several changes of water, but they are boiled and then pulped in ordinary pulping mills, after which they are subjected to drying operations in rotary centrifugal machines until all but 40 per cent of the water has been extracted, the remaining quantity being eliminated in the drying house at a temperature ranging from 100 to 120 deg. F., the hot air currents being circulated by fans. Nitro-cotton forms the principal constituent of a large variety of explosives, the proportion varying according to the nature of the resultant explosive required. For blasting gelatine, 7 per cent soluble nitro-cellulose is used; for cordite, 37 per cent insoluble; ballastite has 60 per cent soluble with 40 per cent nitro-glycerine, etc. In connection with the preparation of the last-named product, use has been made of the curious chemical action that takes place, whereby it may be manufactured by the. "wet process" invented at Ardeer, and which is extremely efficient, and what is far more important, much safer. No matter how much water is present in the tank in which it has been immersed, owing to the extraordinary affinity of the nitro-cotton for the nitro-glycerine, every particle of the cotton will find and receive its full saturation of the nitroglycerine. "Ballastite" is now a popular explosive for sporting and military purposes, being smokeless, clean in the gun, entirely unaffected by heat or dampness, and possessing great ballistic qualities. It is made in several forms, flakes, cubes, or tubes for cannon, and tiny flakes for rifles and sporting guns. When first made and dried it is an elastic paste of a light brown color, but in its final state it resembles thin elastio sheets of silky horn perfectly transparent. This metamorphosis is accomplished by passing the compound through steel rollers heated to 120 deg. F.. which also renders it as thin as tissue paper. It can then be easily cut by machines into the various forms for which it is required. Owing to the worldwide use that is made of the Ardeer products, great care is displayed on the part of the authorities in ascertaining the suitability of the explosive required for any climate. There are 478 two laboratory magazines corresponding to the extremes of temperature, the heat oi" the tropics and the intense cold of the Arctic. These two magazines are appropriately christened "India" and "Siberia" respectively. Of the two, the former is the more dangerous. Before entering the magazine the temperature of the interior is carefully noted through a peephole upon the large thermometer suspended within. In view of the extreme and numerous precautions adopted at these works, accidents are of comparatively rare occurrence. At times, however, catastrophes, despite the measures observed, happen, but they are invariably of a comparatively small character. The rigorous regulations contained in the British Government's Explosives Act passed in 1875 conduce to the safety of the employees. The works are under the management of Mr. C. O. Lundholm, who has been associated for over thirty years with the Nobel works, and with the late Mr. Nobel himself, to whose courtesy we are indebted for the information contained in this article. Although the principal explosive works of the Nobel company are located at Ardeer, distributed over various parts of the country are cognate concerns associated with this Nobel industry, devoted to the manufacture of fuses, detonators, fulminate of mercury, and ammunition for all types of ordnance, so that the Nobel enterprise is in every respect one of the largest and most successful industries in Great Britain.
This article was originally published with the title "The Manufacture of High Explosives" in Scientific American 97, 26, 475-478 (December 1907)